Having read through the docs and tested some stuff out it seems it is recommended to use FoxyCart for the full checkout/registration flow. That's fine by me.
From what I understand the process is something like this:
1. Guest visits our Site
2. Guest goes to subscribe to our services
3. Clicks a subscription plan, using cart=checkout&empty=true we redirect the Guest to the FoxyCart Checkout page
4. Guest punches in valid email/password/confirm password combo, billing info, cc/paypal, hits continue
5. On successful transaction FoxyCart sends instant datafeed to our Endpoint
6. We process it, create a new User on our end linked to the FoxyCart Customer
7. Guest is now a FoxyCart Customer and arrives at FoxyCart Receipt page
Now how do we go from FoxyCart Customer to logged-in User (created in step 6)?
I have a number of ideas of how this could possibly be implemented but I am not sure what is the best way to go about this.
Are there any best practices, recommendations at this point?
Some of the ideas I had are like:
Do we use jsonp somehow to log them in in advance of clicking continue?
Or do we use the continue link itself to do the login when they get back to our site?
How do we do this automatically determining who exactly this person is? Is the receipt id good (secure) enough, but in conjunction with what? How do we identify this person as a Customer->User?